The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium capable of satisfying high density recording and a process for producing the same, and a magnetic recording and reproduction apparatus with the amorphous magnetic recording medium mounted thereon.
With recent progress of diversification of data such as graphics, animation image data, document data, etc., a huge volume of information must be processed. To satisfy processing of such a huge volume of information, it is the most important technical problem in the field of hard discs (magnetic recording and reproduction apparatus) to enhance the surface recording density.
In case of magnetic recording media which shoulders the responsibility of the magnetic recording and reproduction apparatuses as one essential member, it is imperative to reduce the size of magnetic grains to attain the high density recording. However, when the sizes of magnetic grains are reduced to 3 nm or less, depriving of magnetic properties from the once magnetized magnetic grains by thermal energy at room temperature, i.e. so called thermal demagnetization (phenomenon of reduction in magnetism by heat) will be particularly a problem. To prevent the thermal demagnetization, it is necessary to narrow the grain size distribution so as not to form magnetic grains of extremely small grain sizes.
JP-A-6-259743 discloses a method of narrowing the grain size distribution of magnetic grains by using a metal oxide as a metal oxide underlayer; where the grain size distribution of magnetic grains in the magnetic layer is narrowed by providing a metal oxide underlayer by deposition (including vapor deposition and sputtering).
It has been also proposed to make the magnetic layer amorphous to control the magnetic domain of the amorphous magnetic layer to a finer structure. For example, a method of vapor depositing or sputtering amorphous magnetic layers of different magnetic properties (JP-A-2000-67425) and a method of roughening the substrate (JP-A-6-84216).
However, to make epitaxial growth of a magnetic layer of narrow grain size distribution on the underlayer in said JP-A-6-259743, it is necessary to orientate the metal oxide, but the orientation of metal oxide is destroyed, depending on slight deviation from set conditions of a sputter or deviation from a target film composition, resulting in a failure of epitaxial growth of a magnetic layer as an overlayer.
In case of future high density recording such as 40-80 Gb/inch2, the grain sizes will be much smaller, e.g. about 5 nm, and grains of such very smaller grain sizes will be less crystalline, so that it will be very hard to maintain the epitaxial relation.
On the other hand, both said methods of controlling magnetic domains of the amorphous magnetic layer, that is, the method of vapor depositing or sputtering amorphous magnetic layers of different magnetic properties (JP-A-2000-67425) and the method of roughening the substrate (JP-A-6-84216), have not succeeded yet in magnetic domain structure control capable of satisfying the desired 60 Gb/inch2.
An object of the present invention is to provide amorphous magnetic recording media with an amorphous magnetic structure whose magnetic domains are controlled to a fine structure capable of satisfying 60 Gb/inch2.
Another object of the present invention is to provide a magnetic recording and reproduction apparatus using said amorphous magnetic recording medium.